Today's confirmation that Apple is going x86 makes today a historic day in the industry. It may mean that Microsoft might see a few percent decline of their market share the next few years, but what about Linux? If Linux were to lose an equal amount of share it would alter its spread to the desktop, a spread that has been very positive so far.

OS X Apps required the Mac libraries for Quartz and Carbon. These are the GUI and UI stuff. Linux does not have this now and will not have this in the future. Linux uses X11 and things like Gnome or QT (KDE).

These libraries are also excluded from Darwin.

Note: there are some cross platform GUI toolkits like wx that run on windows/macosx/linux and porting apps written with this is trivial.

If all it took was the same CPU then linux/ppc would have tons of mac apps.